High-resolution imaging of contact potential difference with ultrahigh vacuum noncontact atomic force microscope

An ultrahigh vacuum scanning Kelvin probe force microscope (UHV SKPM) utilizing the gradient of electrostatic force, was developed based on an ultrahigh vacuum noncontact atomic force microscope (NC-AFM) capable of atomic level imaging, and used for simultaneous observation of contact potential difference (CPD) and NC-AFM images. CPD images of a Si(111) surface with Au deposited, clearly showed the potential difference in phases between $\text{7×7}$ and $\text{5×2}$ structures. When Ag was deposited as a submonolayer on the Si(111) $\text{7×7}$ reconstructed surface, the atomic level lateral resolution was observed in CPD images as well as in NC-AFM topographic images.